Electrochemical conversion cells, commonly referred to as fuel cells, produce electrical energy by processing first and second reactants. Typically, this is through oxidation of hydrogen and reduction of oxygen, but fuel cells utilizing other reactants (for example, hydrocarbon gas) are also known. By way of illustration and not limitation, one typical type of fuel cell comprises a polymer membrane (e.g., a proton exchange membrane) disposed between a cathode and an anode to form a membrane electrode assembly (MEA). The MEA is positioned between a pair of gas diffusion media layers, and these components are positioned between a cathode plate and an anode plate to form a single cell.
The voltage provided by a single cell is typically too small for many applications, such as powering a vehicle. Therefore, in order to provide for a more suitable quantity of voltage, a plurality of individual cells is typically configured into a “stack.” In such configuration, electrically conductive bipolar plates are positioned between the anode side diffusion layer of one cell and the cathode side diffusion layer of an adjacent cell. The bipolar plates separating adjacent cells serve as current collectors and have opposing surfaces—one surface defining a flow path for conveying fuel (for example, hydrogen or hydrocarbon) to the anode of one cell, and one surfaced defining a flow path for conveying oxidant (for example, oxygen or air) to the cathode of an adjacent cell. Each bipolar plate also has a flow path defined therein for conveying coolant.
The various flow paths of a bipolar plate are connected to corresponding manifolds defined within the plate. For example, the fuel flow path is typically connected to two fuel manifolds, and the oxidant flow path is typically connected to two oxidant manifolds. However, the cross-sectional area of a flow path is significantly smaller than that of a manifold. Accordingly, reactant/coolant flow rates and pressures rise upon entry into a flow path from the manifold. To mitigate against leakage of high pressure reactants and coolant from the fuel cell stack, seals (comprising a seal bead and subgasket) are typically formed between each bipolar plate, and the stack is compressed. Good results have been achieved using elastomeric seal bead materials and thin film polymer subgasket materials that are compatible with the fuel cell environment. Nevertheless, there remains a continuing need for improved ways of sealing between bipolar plates, particularly those that can reduce the complexity and cost of manufacturing fuel cell stacks.